1. Field of the Invention
The present invention relates to the field of matrix-assisted laser desorption and ionization (MALDI) mass spectrometry, and more particularly relates to the field of sample plates for MALDI.
2. Discussion of Related Art
Matrix-assisted laser desorption and ionization (MALDI) has proven to be one of the most successful ionization methods for mass spectrometric analysis and investigation of large molecules. The sample to be ionized and analyzed by mass spectrometry is embedded in a solid matrix that greatly facilitates the production of intact gas-phase ions from large, nonvolatile, and thermally labile compounds such as proteins, oligonucleotides, synthetic polymers, and large inorganic compounds. A laser beam (UV- or IR-pulsed laser) serves as the desorption and ionization source. The matrix molecules play a key role in this technique by absorbing the laser light energy and causing sample molecules to be ablated from a portion of the matrix surface. Once the sample molecules are vaporized and ionized they are transferred by ion optics into a mass spectrometer for mass analysis, typically by operation of an ion trap or time-of-flight (TOF) mass analyzer.
In commercial MALDI mass spectrometer instruments, a large number of sample spots are deposited on a sample plate to enable rapid and efficient analysis of multiple samples. MALDI sample plates are typically formed of stainless steel having a highly polished and flat surface. The plates may be adapted to fit into and to be handled by automated handling apparatus employed to transport and position the plates within the mass spectrometer instrument, and optionally to transport the plates between different stations in an automated analysis train (e.g., between automated sample deposition equipment and the mass spectrometer). To enable their use in automated handling apparatus and also to conform their size to standardized dimensions required by other equipment, MALDI sample plates have traditionally been integrated with a base structure. Because a sample plate body consisting of an integral metallic sample plate and base structure is expensive to manufacture, others in the art have proposed alternative constructions. For example, U.S. Pat. No. 6,670,609 to Franzen et al. describes a sample plate assembly consisting of a sample plate permanently bonded to a base structure by a set of cooperating pins and holes. The bonding arrangement purportedly accommodates the differential thermal expansion of the sample plate and base structure, which may be fabricated from different materials. Disposable single-use MALDI plates fabricated from relatively low-cost materials have also been developed as an alternative to conventional sample plates. However, the sample plate construction disclosed in the aforementioned Franzen patent, as well as other alternatives known in the art, generally fail to provide the degree of rigidity and planarity required for reliable operation in a MALDI mass spectrometer.